This project is directed toward the detection of functional changes in the cardiovascular system associated with compounds of environmental significance to which toxicologically significant exposure would be expected by inhalation. The cardiovascular effects of brief inhalation exposures of rabbits and guinea pigs to 100 ppm of morpholine of the IV injection of micromolar quantities of the liquid in aqueous solution were unremarkable. The mechanism of a transitory hypotension associated with the presumed activation of vascular muscarinic receptors remained incompletely described.